Coating agent based on polymers containing carboxyl groups and crosslinking agents containing epoxide groups, processes for the preparation of the coating agent and its use

ABSTRACT

The present invention relates to coating agents containing 
     A) one or more polymers containing carboxyl groups and having a number-average molecular weight of 500 to 8,000 and an acid number of 15 to 200 mg of KOH/g as the essential binder component and 
     B) one or more compounds containing epoxide groups as crosslinking agents, 
     wherein the compound B containing epoxide groups is a copolymer containing epoxide groups, has a number-average molecular weight M n  of 300 to 5,000, preferably 500 to 3,500, and a heterogeneity (M w  /M n ), measured by gel permeation chromatography, of ≦3, preferably of ≦2, and has been prepared by continuous bulk polymerization at temperatures between 130° and 350° C. and pressures above 1 bar. 
     The invention also relates to processes for the preparation of the coating agent and the use of the coating agents in automobile refinishing.

The invention relates to coating agents containing

A) one or more polymers containing carboxyl groups and having anumber-average molecular weight M_(n) of 500-8,000 and an acid number of15 to 200 mg of KOH/g as the essential binder component and

B) one or more compounds containing epoxide groups as the crosslinkingagent.

Coating agents which contain polymers containing carboxyl groups as thebinder and compounds containing epoxide groups as the crosslinking agentare known and are described, for example, in international PCTpublication WO 87/02041, EP-A-103,199, EP-B-51,275, EP-A-123,793, DE-AS2,635,177, Japanese Preliminary Published Specification 219,267/83,Japanese Preliminary Published Specification 76,338/77 and JapanesePreliminary Published Specification 53,145/79.

If these coating agents based on polymers containing carboxyl groups andepoxide compounds are to be hardened at low temperatures (that is to say≦80° C.), this requires the use of highly reactive epoxide compounds.However, such epoxide compounds based on aliphatic epoxides have usuallyproved to be mutagenic in the Ames test. This is to be attributed on theone hand to high contents of oligomeric constituents, but on the otherhand also to the preparation process, that is to say the reaction withepichlorohydrin and the associated residual content of epichlorohydrin.

Epoxide compounds which are less toxicologically unacceptable areusually very high molecular weight compounds and are therefore lessreactive, or they are built up on the basis of bisphenol A or bisphenolF and are unsuitable for use as a top or clear coat because of theirtendency to yellow. Finally, acrylate copolymers which contain epoxidegroups and have been prepared by conventional methods are likewiseunsuitable for toxicological reasons, because of their high content ofresidual monomers.

The disadvantage of the known coating agents based on polymerscontaining carboxyl groups and epoxy crosslinking agents is moreoveroften the high viscosity of the coating agents and thus the low solidscontent of the coating agents at a viscosity which is advantageous forprocessing. This leads to high pollution of the environment with solventduring drying of the coating films.

Low-solvent stoving lacquers which consist of acrylate resin containingcarboxyl groups, epoxy resin containing at least 2 oxirane groups permolecule, solvents and if appropriate pigment, catalyst and otherauxiliaries are thus known from DE-PS 2,728,459. The acrylate resincontaining carboxyl groups which is employed as the binder is preparedin bulk by means of free radical polymerization under pressures of 1.5to 30 bar at temperatures of 160° to 280° C. and is distinguished by alow heterogeneity, measured by gel permeation chromatography, of between1.5 and 2.0 and a number-average molecular weight of 1,500 to 3,000.However, since the epoxide compounds based on bisphenol A or compoundsprepared using epichlorohydrin or acrylate copolymers containing epoxidegroups which are usually employed are used as the crosslinking agent,these stoving enamels also have the abovementioned disadvantages causedby these crosslinking agents, such as a tendency to yellow and/ortoxicity.

The preparation of acrylate copolymers containing functional groups,such as, for example, hydroxyl, carboxyl, epoxide, isocyanate or aminogroups, and having only a low dispersity, a low number-average molecularweight of 500 to 6,000 and a low viscosity of the resulting solutions ofthe acrylate copolymers is also known from EP-A-96,901. The acrylatecopolymers are prepared by means of a continuous bulk polymerizationprocess, if appropriate under pressure, at polymerization temperaturesbetween 180° and 270° C.

Coating agents which contain acrylate copolymers containing hydroxylgroups and prepared by the process of EP-A-96,901 as binders and urearesins, melamine resins or benzoguanamine resins as well aspolyisocyanates or polyepoxides as crosslinking agents are alsodescribed in EP-A-96,901.

The present invention provides coating agents which are based onpolymers containing carboxyl groups as crosslinking agents and can behardened at such low temperatures (about≦80° C.) that they are suitablefor car refinish. The coating agents should also have the lowestpossible solvent content at a viscosity favorable for processing, whichis 16 to 20 s measured in a flow cup according to DIN 4 at 23° C. Thecoating agents should moreover be as acceptable as possible from thetoxicology point of view, that is to say in particular they should havethe lowest possible residual monomer content. The coating agents shouldand be usable both as a primer and as a top and/or clear coat, that isto say they should lead to coatings which have only a slight tendency orno tendency at all to yellow. Finally, the coating agents should exhibita good flow and a low tendency to run even on vertical surfaces, andlead to coatings having a good gloss and good hardness, coupled withgood flexibility and good resistance to chemicals.

Surprisingly, this object is achieved by a coating agent containing

A) one or more polymers containing carboxyl groups and having anumber-average molecular weight M_(n) of 500-8,000 and an acid number of15 to 200 mg of KOH/g as the essential binder component and

B) one or more compounds containing epoxide groups as crosslinkingagents.

The coating agent contains a compound B containing epoxide groups whichis a copolymer containing epoxide groups, has a number-average molecularweight M_(n) of 300 to 5,000, preferably 500 to 3,500, and aheterogeneity (M_(w) /M_(n)), measured by gel permeation chromatography,of ≦3, preferably of ≦2, and has been prepared by continuous bulkpolymerization at temperatures between 130° and 350° C. and pressuresabove 1 bar.

The present invention furthermore also relates to a process for thepreparation of the coating agents and the use of the coating agents incar repair lacquering, as a primer, top lacquer or clear lacquer.

It is surprising and was not predictable that the coating agentsaccording to the invention can be processed with high solids contents ofup to 80% by weight at a spray viscosity of 16 to 20 seconds, measuredin a flow cup according to DIN 4 at 23° C., are less toxicologicallyunacceptable than conventional comparable coating agents, exhibit a goodflow and a low tendency to run, even on vertical surfaces, and lead tocoatings which can be hardened at low temperatures (≦80° C.) and exhibita good gloss and good hardness, coupled with a good elasticity and goodresistance to chemicals.

The preparation of the compounds containing epoxide groups employed ascrosslinking agent B will first be explained in more detail below,followed by the preparation of the polymers containing carboxyl groupsemployed as binder A and the preparation of the coating agents usingcomponents A and B.

The compounds containing epoxide groups employed as crosslinking agentsin the coating agents according to the invention are prepared by meansof continuous bulk polymerization at temperatures between 130° and 350°C. and pressures above 1 bar, as a rule under pressures between 2 and200 bar, preferably under pressures between 5 and 120 bar. Thecontinuous bulk polymerization process is known per se and is described,for example, in EP-A-96,901. The polymerization process will thereforebe explained only briefly, and reference is made to EP-A-96,901 forfurther details.

The copolymers containing epoxide groups employed according to theinvention are prepared in pressure apparatuses, such as, for example,pressure kettles, pressure kettle cascades, pressure tubes with andwithout mixing elements or else in pressure kettles in combination withpressure tubes. The pressure kettles can be equipped with various mixingunits, such as stirrers or a mixing circulation with a circulation pump.The pressure apparatuses are furthermore provided with devices forregulation of the temperature of the contents of the reactor, such as,for example, internal cooling or heating coils or a cooling or heatingjacket. The amount of heat liberated during the polymerization canmaintain the temperature required for the polymerization, or it isnecessary to heat or cool the reaction zone, depending on the monomercomposition and depending on the amount of monomers fed in per unittime.

To carry out the polymerization reaction, the various monomers areeither mixed before introduction into the polymerization reactor and themixture is then metered into the reactor, or else the various monomersare metered into the reactor individually in the desired ratio with theaid of pumps. The copolymerization is then carried out in polymerizationreactors having low contents, so that a stable state is already reachedshortly after the start of the polymerization. In this way it is alsopossible for one type of copolymer to be changed to another withoutproblems and rapidly.

The residence time of the reaction mixture in the polymerizationapparatuses is 2 to 60 minutes. Preferably, however, an averageresidence time--defined as the reactor volume divided by the volume ofmonomer mixture fed in per unit time--of 10 to 40 minutes is preferablymaintained.

A preferred embodiment of the bulk polymerization process comprisesproducing periodic pressure variations in the polymerization reactorduring the polymerization, as described, for example, inDE-OS-3,026,831. The periodic pressure variations with a pressuredifference of 15 to 100 bar at a frequency of the pressure variations of6 to 300 per hour are generated, for example, by forcing in an inert gasperiodically and then ensuring the reactor is let down, or, for example,by program-controlled regulation of the maintenance of the pressure withthe aid of customary devices. The program control can be based on, forexample, sine oscillation or saw-tooth oscillation with amplitudes inthe stated pressure limits and frequencies of 6 to 300 oscillations perhour.

Because of the periodic pressure variations in the polymerizationapparatus, a pulsed flow of the reaction mixture also occurs in this.The polymer formed thus has a varying residence time spectrum, which inturn results in a broader chemical and physical uniformity than in thenon-pulsed procedure. The pulsed flow within the polymerizationapparatus moreover avoids caking and thermal damage of the copolymer inthe reactor. The bulk polymerization reaction can be carried out eitherwithout initiators or in the presence of 0.01 to 5% by weight, based onthe weight of monomers employed, of a suitable initiator.

Suitable free radical initiators are organic peroxides, such as, forexample, dibenzoyl peroxide, dicumyl peroxide, cumene hydroperoxide,di-tert.-butyl peroxide, tert.-butyl amyl peroxide, tert.-butylhydroperoxide, 2,2-di-tert.-butylperoxybutane, tert.-amyl perbenzoate,1,3-bis(tert.-butylperoxyisopropyl)-benzene, diisopropylbenzenemonohydroperoxide and diacyl peroxides, such as, for example, diacetylperoxide, peroxyketal, such as, for example,2,2-di(tert.-amylperoxy)-propane and ethyl3,3-di-(tert.-amylperoxy)-butyrate, and thermally unstable highlysubstituted ethane derivatives, for example based on silyl-substitutedethane derivatives and based on benzopinacol. Aliphatic azo compounds,such as, for example, azobiscyclohexanenitrile, can furthermore also beemployed.

The polymerization reaction is advantageously carried out withoutpolymerization regulators. The molecular weight of the copolymerscontaining epoxide groups which have been prepared is rather controlledon the one hand via the polymerization temperature and on the other handvia the amount added of monomers having at least 2 ethylenicallyunsaturated double bonds.

The polymerization is preferably carried out in the absence of solvents.However, it is also possible to add small amounts (up to 20% by weight,based on the monomer mixture) of solvents in order thus to control thepolymerization. Solvents which are particularly suitable for this arethose which react with at least one of the monomers, such as, forexample, ethylene glycol, propylene glycol and the like. The copolymersB containing epoxide groups which are prepared by the bulkpolymerization process have number-average molecular weights M_(n) ofbetween 300 and 5,000, preferably between 500 and 3,500, and aheterogeneity (weight-average molecular weight M_(w) /number-averagemolecular weight M_(n)), measured by gel permeation chromatography, of≦3, preferably ≦2. The heterogeneity is measured here by generally knownmethods (compare, for example, B. Vollmert, Grundriβ dermakromolekularen Chemie (Principles of macromolecular chemistry), E.Vollmert-Verlag, Karlsruhe 1982, Volume III, page 72 et seq.) against apolystyrene standard.

These copolymers B containing epoxide groups are prepared bycopolymerization of

a) 10 to 60% by weight, preferably 15 to 50% by weight, of one or morevinylaromatic hydrocarbons,

b) 10 to 50% by weight, preferably 15 to 30% by weight, of one or moreethylenically unsaturated monomers containing at least one epoxide groupper molecule and

c) 5 to 80% by weight, preferably 20 to 50% by weight, of otherethylenically unsaturated copolymerizable monomers,

the sum of the weight contents of components a to c in each case being100% by weight.

Component a is a monovinylaromatic compound. It preferably contains 8 or9 carbon atoms per molecule. Examples of suitable compounds are styrene,vinyltoluenes, α-methylstyrene, chlorostyrenes, o-, m- orp-methylstyrene, 2,5-dimethylstyrene, p-methoxystyrene,p-tert.-butylstyrene, p-dimethylaminostyrene, p-acetamidostyrene andm-vinylphenol. Vinyltoluenes and in particular styrene are preferablyemployed.

Examples of monomers having at least one epoxide group per molecule(component b) are glycidyl acrylate, glycidyl methacrylate, allylglycidyl ether, glycidyl crotonate, glycidyl α-ethylacrylate andcrotonyl glycidyl ether. Glycidyl methacrylate and/or glycidyl acrylateare preferably employed.

Compounds which are particularly suitable as component c are alkylesters of acrylic and methacrylic acid, such as, for example, methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl(meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate,pentyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate,cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl(meth)acrylate, 3,5,5-trimethylhexyl (meth)acrylate, decyl(meth)acrylate, dodecyl (meth)acrylate, hexadecyl (meth)acrylate,octadecyl (meth)acrylate and octadecenyl (meth)acrylate.

Other ethylenically unsaturated monomers can preferably be employedtogether with these alkyl esters of acrylic and methacrylic acid, butalso exclusively as component c, the choice of these monomers largelydepending on the desired properties of the coating agents in respect ofhardness, elasticity, compatibility and polarity.

Examples of other suitable ethylenically unsaturated monomers are thealkyl esters of maleic, fumaric, tetrahydrophthalic, crotonic,isocrotonic, vinylacetic and itaoonic acid, such as, for example, thecorresponding methyl, ethyl, propyl, butyl, isopropyl, isobutyl, pentyl,amyl, isoamyl, hexyl, cyclohexyl, 2-ethylhexyl, octyl,3,5,5-trimethylhexyl, decyl, dodecyl, hexadecyl, octadecyl andoctadecenyl esters.

Small amounts of monomers containing at least two polymerizableolefinically unsaturated double bonds can furthermore also be employed.The content of these monomers is preferably less than 5% by weight,based on the total weight of the monomers. Examples of suitablecompounds are the compounds listed on pages 27 to 28 of thisdescription.

The resulting copolymers containing epoxide groups in general haveepoxide equivalent weights of 150 to 2,000, preferably 500 to 1,000.

The small amounts of monomers which may still be present are preferablyremoved from the polymer--for example by distillation--directly afterthe bulk polymerization reaction. In contrast to the preparation ofcopolymers by means of solution polymerization, because of the absenceof solvents in the copolymers prepared by the bulk polymerizationprocess this takes place quite without problems. To prepare the coatingagents according to the invention, the copolymers containing epoxidegroups are usually dissolved in one or more organic solvents. Thiscrosslinking agent solution is then mixed with the binder solution onlyimmediately before application of the coating agents. Examples ofsolvents which are suitable for dissolving the copolymers containingepoxide groups are relatively highly substituted aromatics, such as, forexample, Solvent Naphtha®, heavy benzene, various Solvesso® grades,various Shellsol® grades and Deasol, higher-boiling aliphatic andcycloaliphatic hydrocarbons, such as, for example, various whitespirits, mineral turpentine oil, tetralin and decalin, as well asesters, such as, for example, butyl acetate, pentyl acetate, ethoxyethylpropionate and 1-methoxypropyl 2-acetate. Mixtures of various solventscan of course also be employed.

The coating agents according to the invention contain as essentialbinder component one or more polymers containing carboxyl groups andhaving a number-average molecular weight M_(n) of 500 to 8,000 and anacid number of 15 to 200 mg of KOH/g, preferably 30 to 120 mg of KOH/g.The carboxyl groups can be introduced here directly by using unitscontaining carboxyl groups when building up the polymers However, it isalso possible for a polymer containing hydroxyl and if appropriatecarboxyl groups and having an OH number of 15 to 200 mg of KOH/g firstto be built up and for all or some of the carboxyl groups to beintroduced in a second stage by reaction of the polymers containinghydroxyl and if appropriate carboxyl groups with carboxylic acidanhydrides.

Carboxylic acid anhydrides which are suitable for addition onto thepolymers containing hydroxyl groups are the anhydrides of aliphatic,cycloaliphatic and aromatic saturated and/or unsaturated di- andpolycarboxylic acids, such as, for example, the anhydrides of phthalicacid, tetrahydrophthalic acid, hexahydrophthalic acid, succinic acid,maleic acid, itaconic acid, glutaric acid, trimellitic acid andpyromellitic acid, and halogenated or alkylated derivatives thereof.

Anhydrides of phthalic acid and tetrahydro- and hexahydrophthalic acidand 5-methylhexahyirophthalic anhydride are preferably employed.

The polymers containing hydroxyl groups are reacted with the carboxylicacid anhydrides at temperatures of 50° to 140° C. in the presence of acatalyst, such as, for example, tertiary amines.

The polymers containing carboxyl groups are copolymers containingcarboxyl groups and/or polyesters containing carboxyl groups. Thepolyesters containing carboxyl groups can be built up by the customarymethods (compare, for example, B. Vollmert, Grundriβ dermakromolekularen Chemie (Principles of macromolecular chemistry), E.Vollmert-Verlag Karlsruhe 1982, Volume 11, page 5 et seq.) fromaliphatic and/or cycloaliphatic alcohols which contain two, three ormore functional groups, if appropriate together with monohydricalcohols, and from aliphatic and/or cycloaliphatic carboxylic acids andpolycarboxylic acids containing a higher number of functional groups.Examples of suitable alcohols are ethylene glycol, 1,2-propanediol,1,3-propanediol,2,2-dimethyl-1,3-propanedio1,1,2-butanedio1,1,3-butanediol,1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol,1,6-hexanediol, 2-ethyl-1,6-hexanediol, 2,2,4-trimethyl-1,6-hexanediol,1,4-dimethylolcyclohexane, glycerol, trimethylolethane,trimethylolpropane, pentaerythritol, etherification products of diolsand polyols, for example di- and triethylene glycol, polyethylene glycoland the neopentyl glycol ester of hydroxypivalic acid.

Examples of suitable carboxylic acids are adipic, azelaic,tetrahydrophthalic, hexahydrophthalic andendomethylenetetrahydrophthalic acid, and derivatives thereof which arecapable of esterification.

The polyesters containing carboxyl groups which are employed in thecoating agents according to the invention can contain tertiary aminogroups if appropriate. These tertiary amino groups can be introducedinto the polymer in the most diverse ways. On the one hand, carboxylicacids and/or alcohols containing tertiary amino groups can be employedwhen building up the polyesters, and on the other hand the tertiaryamino groups can also be introduced in a second stage. This can becarried out, for example, by reaction of polymers containing hydroxylgroups with carboxylic acids which contain a tertiary amino group orwith compounds which contain on average 0.8 to 1.5, preferably one, freeisocyanate group and at least one tertiary amino group per molecule. Thepolymers containing carboxyl groups can furthermore also be reacted withcompounds which, in addition to a tertiary amino group, also contain analcohol, thiol or primary or secondary amino group.

However, acrylate copolymers containing carboxyl groups, if appropriatein combination with the polyesters containing carboxyl groups, arepreferably employed as the polymers containing carboxyl groups. Suitablecopolymers containing carboxyl groups can be prepared either with theaid of free radical solution polymerization or by means of continuousbulk polymerization.

Suitable polymers A containing carboxyl groups are thus, for example,copolymers which have been prepared by continuous bulk polymerization attemperatures between 130° and 350° C. under pressures above 1 bar, as arule under pressures between 2 and 200 bar, preferably under pressuresbetween 5 and 120 bar. The bulk polymerization process proceedsanalogously to the bulk polymerization process for the preparation ofthe copolymers B containing epoxide groups.

The copolymers containing carboxyl groups which are prepared by means ofbulk polymerization have a heterogeneity (M_(w) /M_(n)), determined bygel permeation chromatography, of ≦3.5, preferably ≦2, and a K value(according to Fikentscher) of less than 20, preferably less than 15, aswell as acid numbers of 15 to 200 mg of KOH/g, preferably 30 to 120 mgof KOH/g, and amine numbers of 0 to 50 mg of KOH/g, preferably 10 to 40mg of KOH/g.

The copolymers A are prepared by bulk polymerization of

m₁) 1 to 30% by weight, preferably 10 to 25% by weight, of one or moreethylenically unsaturated monomers containing carboxyl groups,

m₂) 0 to 50% by weight, preferably 10 to 30% by weight, of one or morealkyl esters of acrylic and/or methacrylic acid,

m₃) 5 to 80% by weight, preferably 10 to 50% by weight, of one or morevinylaromatic hydrocarbons,

m₄) 0 to 40% by weight, preferably 5 to 25% by weight, of one or morehydroxyalkyl esters of α,β-unsaturated carboxylic acids and

m₅) 0 to 70% by weight of other ethylenically unsaturatedcopolymerizable monomers,

the sum of the amounts by weight of components m₁ to m₅ always being100% by weight.

All or some of the carboxyl groups can of course also be introduced byreaction of a copolymer containing hydroxyl groups with carboxylic acidanhydrides. Examples of suitable monomers m₁ containing carboxyl groupsare unsaturated carboxylic acids, such as, for example, acrylic,methacrylic, itaconic, crotonic, isocrotonic, aconitic, maleic andfumaric acid, half-esters of maleic and fumaric acid as well asβ-carboxyethyl acrylate and adducts of hydroxyalkyl esters of acrylicacid and/or methacrylic acid with carboxylic acid anhydrides, such as,for example, mono-2-methacryloyloxyethyl phthalate.

Examples of suitable alkyl esters of acrylic and methacrylic acid(component m₂) are the compounds already listed as suitable componentsc.

Vinylaromatic compounds which are suitable as component m₃ are thecompounds already listed as component a.

Possible components m are hydroxyalkyl esters of α,β-unsaturatedcarboxylic acids containing primary or secondary hydroxyl groups.Hydroxyalkyl esters containing primary hydroxyl groups are predominantlyemployed, since they have a higher reactivity in the polymer-analogousreaction with the carboxylic acid anhydride. Mixtures of hydroxyalkylesters containing primary hydroxyl groups and hydroxyalkyl esterscontaining secondary hydroxyl groups can of course also be used, forexample if hydroxyl groups are required in the copolymer containingcarboxyl groups, for example for adjusting the compatibility of thecopolymer containing carboxyl groups.

Examples of suitable hydroxyalkyl esters of α,β-unsaturated carboxylicacids containing primary hydroxyl groups are hydroxyethyl acrylate,hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyamyl acrylate,hydroxyhexyl acrylate, hydroxyoctyl acrylate and the correspondingmethacrylates. Examples which may be mentioned of hydroxyalkyl esterswhich contain a secondary hydroxyl group and which can be used are2-hydrox-ypropyl acrylate, 2-hydroxybutyl acrylate, 3-hydroxybutylacrylate and the corresponding methacrylates.

The corresponding esters of other α,β-unsaturated carboxylic acids, suchas, for example, of crotonic acid and of isocrotonic acid, can of coursein each case also be employed.

At least some of component m₄ can advantageously be a reaction productof one mole of hydroxyethyl acrylate and/or hydroxyethyl methacrylateand on average two moles of ε-caprolactone.

A reaction product of acrylic acid and/or methacrylic acid with theglycidyl ester of a carboxylic acid containing a tertiary α-carbon atomcan also be employed as at least some of component m₄. Glycidyl estersof highly branched monocarboxylic acids are obtainable under thetradename "Cardura". The reaction of the acrylic acid or methacrylicacid with the glycidyl ester of a carboxylic acid containing a tertiaryα-carbon atom can be carried out before, during or after thepolymerization reaction.

The choice of the other ethylenically unsaturated monomers m₅ is notparticularly critical. However, it should be ensured that theincorporation of these monomers does not lead to undesirable propertiesof the copolymer. The choice of components m₅ thus largely depends onthe desired properties of the hardenable composition in respect ofelasticity, hardness, compatibility and polarity.

Examples of suitable compounds as component m₅ are alkoxyethylacrylates, aryloxyethyl acrylates and the corresponding methacrylates,such as, for example, butoxyethyl (meth)acrylate and phenoxyethyl(meth)acrylate, unsaturated compounds containing tertiary amino groups,such as, for example, N,N'-diethylaminoethyl methacrylate,2-vinylpyridine, 4-vinylpyridine, vinylpyrroline, vinylquinoline,vinylisoquinoline, N,N'-dimethylaminoethyl vinyl ether and2-methyl-5-vinylpyridine; compounds, such as, for example acrylonitrile,methacrylonitrile, acrolein and methacrolein.

Monomers containing at least two polymerizable double bonds canfurthermore also be employed as component m₅, if appropriate togetherwith other monomers of those just listed. Examples of suitable compoundsare the compounds listed on pages 27 and 28 of this description. Thesemonomers containing at leasts 2 double bonds are employed in smallamounts, preferably in an amount of up to 5% by weight, based on thetotal weight of the monomers.

It is particularly advantageous for tertiary amino groups to beincorporated into the copolymer containing carboxyl groups, since theycatalyze subsequent crosslinking of the polymer containing carboxylgroups with epoxide groups and in this way lower the stovingtemperatures of coating agents based on these polymers.

If the copolymer contains tertiary amino groups, during the addition ofunsaturated carboxylic acid anhydrides, such as, for example, during theaddition of maleic anhydride, it must be ensured that no solvents whichreact with the unsaturated carboxylic acid anhydride under catalysis bythe tertiary nitrogen groups are employed Acetone, methyl ethyl ketone,butyl acetate and other acetylating solvents, for example, thereforecannot be used. Hydrocarbons and polar solvents, such asdimethylformamide, dimethylacetamide, N-methylpyrrolidone etc., can beused.

The tertiary amino groups can be incorporated into the copolymer by useof monomers containing tertiary amino groups as component m₅.

Preferably, however, the tertiary amino groups are introduced byreaction of the polymer containing hydroxyl and carboxyl groups withcompounds V which contain on average 0.8 to 1.5, preferably one, freeisocyanate group and at least one tertiary amino group per molecule.However, it is also possible for the copolymer containing hydroxylgroups first to be reacted with the compounds V and only then for thecarboxyl groups to be introduced into the copolymer by reaction with acarboxylic acid anhydride. In this case--as already mentioned--thereaction with the anhydride can be carried out at lower temperatures.

The amount of compound V is chosen here so that the resin formed has anamine number of 0 to 50 mg of KOH/g. If the copolymers are to beemployed in coating agents which are hardened at room temperature, ahigher amine number of 10 to 40 mg of KOH/g is established.

The compounds V used to introduce the tertiary amino group are preparedby reacting diisocyanates or polyisocyanates with less than thestoichiometric amount of a tertiary amine. Tertiary amines of thegeneral formula NR₁ R₂ R₃, wherein R₁ preferably denotes an alkanolradical or another radical containing hydroxyl groups and R₂ or R₃ canrepresent alkyl or cycloalkyl radicals, are suitable for this reaction.Dialkylalkanolamines, such as, for example, dimethylethanolamine,diethylethanolamine and higher homologs or isomers thereof, arepreferred.

Examples of suitable di- or polyisocyanates are: aromatic isocyanates,such as, for example, toluylene 2,4- and 2,6-diisocy,anate and mixturesthereof, diphenylmethane 4,4'-diisocyanate, m-phenylene diisocyanate,p-phenylene diisocyanate, diphenyl 4,4'-diisocyanate, naphthalene1,5-diisocyanate, naphthalene 1,4-diisocyanate, toluidine4,4'-diisocyanate, xylylene diisocyanate and substituted aromaticsystems, such as, for example, dianisidine diisocyanates, diphenyl ether4,4'-diisocyanates or chlorodiphenyl diisocyanates, and aromaticisocyanates containing a higher number of functional groups, such as,for example, 1,3,5-triisocyanatobenzene,4,4',4"-triisocyanatotriphenylmethane, 2,4,6-triisocyanatotoluene and4,4'-diphenyldimethylmethane 2,2',5,5'-tetraisocyanate; cycloaliphaticisocyanates, such as, for example, cyclopentane 1,3-diisocyanate,cyclohexane 1,4-diisocyanate, cyclohexane 1,2-diisocyanate andisophorone diisocyanate, and aliphatic isocyanates, such as, forexample, trimethylene 1,6-diisocyanate, tetramethylene 1,6-diisocyanate,pentamethylene 1,6-diisocyanate, hexamethylene 1,6-diisocyanate,trimethylhexamethylene 1,6-diisocyanate and tris-hexamethylenetriisocyanate.

Diisocyanates containing isocyanate groups of different reactivity arepreferably employed, such as, for example, isophorone diisocyanate.

The reaction between the amine and the isocyanate is carried out attemperatures of 0° to 80° C., preferably of 20° to 50° C. Thequantitative proportions of the reaction partners are chosen so that thecompound V formed contains 0.8 to 1.5, preferably 1, free isocyanategroups.

In addition, there is also the possibility of reacting the copolymercontaining hydroxyl and if appropriate carboxyl groups with carboxylicacids which contain a tertiary nitrogen atom. Examples of suchcarboxylic acids are 3- and 4-dimethylaminobenzoic acid, picolinic acidand dimethylaminosalicylic acid.

Finally, it is also possible for tertiary amino groups to be introducedinto the copolymer containing carboxyl groups by reaction of some of thecarboxyl groups and if appropriate carboxylic acid anhydride groups ofthe copolymer with compounds which, in addition to a tertiary aminogroup, also contain an alcohol or primary or secondary amino group or athiol group.

Examples of alcohols containing tertiary amino groups are adducts ofsecondary amines and epoxide compounds. Examples of suitable secondaryamines are dimethylamine, diethylamine, dipropylamine, dibutylamine,morpholine and pyrrolidine.

Examples of suitable epoxide compounds are ethylene oxide, propyleneoxide, butylene oxide, styrene oxide and cyclohexene oxide.

Suitable alcohols which contain tertiary amino groups and are obtainedby reaction of secondary amines with epoxide compounds aredimethylaminoethanol, diethylaminoethanol, di-n-propylaminoethanol,diisopropylaminoethanol, di-n-butylaminoethanol,N-(2-hydroxyethyl)morpholine, N-(2-hydroxyethyl)piperidine,N-(2-hydroxyethyl)pyrrolidone, N-(2-hydroxyethyl)aziridine,N,N'-dimethyl-2-hydroxypropylamine, N,N'-diethyl-2-hydroxypropylamine,triethanolamine and tripropanolamine.

Other examples of alcohols containing tertiary amino groups are vinylpolymers which have both a tertiary amino group as well as a hydroxylgroup in the side chain and are obtainable by copolymerization of the(meth)acrylate monomers mentioned containing tertiary amino groups withmonomers containing OH groups, such as, for example, β-hydroxyethyl(meth)acrylate.

Examples of the primary or secondary amines which contain a tertiaryamino group are N,N'-dialkyl-1,3-propylenediamines, such as, forexample, N,N'-dimethyl-1,3-propylenediamine,N,N'-diethyl-1,3-propylenediamine andN,N'-dialkyl-1,4-tetramethylenediamines, such as, for example,N,N'-dimethyl-1,4-tetramethylenediamine andN,N'-diethyl-1,4-tetramethylenediamine.N,N'-Dialkyl-1,6-hexamethylenediamines and N-alkylpiperazines as well as2-aminopyridine, 4-aminopyridine and N-alkylaminopyridine arefurthermore possible.

The tertiary amino groups can of course also be introduced into thecopolymer A by a combination of various methods.

The copolymers which contain carboxyl groups and are employed as theessential binder component A in the coating agents according to theinvention can also be prepared by means of free radical solutionpolymerization. Suitable copolymers containing carboxyl groups aretherefore also the copolymers which contain carboxyl groups and aredescribed in the PCT application with the international publicationnumber WO 87/02041. These acrylate copolymers containing carboxyl groupsare prepared by polymerization of the monomers in an organic solvent attemperatures between 70° and 130° C., preferably between 80° and 120°C., preferably using at least 0.5% by weight, preferably at least 2.5%by weight, based on the total weight of the monomers, of apolymerization regulator and in the presence of 0.5 to 7% by weight,based on the total weight of the monomers, of a polymerizationinitiator.

The polymerization is carried out in an organic solvent which is inerttowards the monomers employed and towards carboxylic acid anhydridesExamples of suitable solvents are glycol ethers, such as, for example,diglycol dimethyl ether; aromatics, such as, for example, toluene,xylene, Solvent Naphtha®, heavy benzene, various Solvesso® grades,various Shellsol® grades and Deasol, as well as higher-boiling aliphaticand cycloaliphatic hydrocarbons, such as, for example, various whitespirits, mineral turpentine oil, tetralin and decalin.

If the copolymer contains tertiary amino groups, it must be ensured thatno solvents which react with the unsaturated carboxylic acid anhydrideunder catalysis by the tertiary amino groups are employed.

The reaction is preferably carried out in the presence of polymerizationregulators, since clouding of the polymer solutions can be avoided moreeasily in this way. Preferred suitable regulators are mercaptocompounds, mercaptoethanol being particularly preferably employed.Examples of other possible regulators are alkylmercaptans, such as, forexample, t-dodecylmercaptan, octylmercaptan, phenylmercaptan,octyldecylmercaptan and butylmercaptan, and thiocarboxylic acids, suchas, for example, thioacetic acid or thiolactic acid.

The regulators are preferably dissolved in one of the monomer feeds andadded together with the monomers. Suitable free radical initiators arethe compounds in the description of the bulk polymerization. Othersuitable initiators are azo initiators, such as, for example,azoisobutyronitrile, 2,2'-azobis(2-methylbutane-nitrile),1,1'-azobis(cyclohexanecarbonitrile) and2,2'-azobis(2-dimethylbutane-nitrile). The choice of the particularinitiator depends here on the reaction conditions. If more than 1% byweight of mercaptan, based on the total weight of the monomers, isemployed, non-oxidizing initiators are preferably employed. Theinitiator, dissolved in some of the solvent employed for thepolymerization, is gradually metered in during the polymerizationreaction The initiator feed preferably lasts about 0.5 to 1 hour longerthan the monomer feed, so that a good action is thus also achievedduring the after-polymerization phase. If initiators having a longhalf-life under the reaction temperatures which exist are employed, itis also possible for the initiator to be initially introduced into thevessel.

The copolymers containing carboxyl groups can be prepared by thesolution polymerization just described of

1₁) 0 to 30% by weight, preferably 5 to 20% by weight, of one or moremonomers containing carboxyl groups,

1₂) if appropriate more than 3 to 30% by weight, preferably 5 to 25% byweight, of one or more monomers containing at least two polymerizableolefinically unsaturated double bonds and

1₃) at least 40% by weight of other copolymerizable ethylenicallyunsaturated monomers, the sum of the parts by weight of components 1₁ to1₃ in each case being 100% by weight.

The properties of the copolymers containing carboxyl groups, such as,for example, solubility, can be selectively controlled by using monomers1₂ containing at least two polymerizable double bonds. However,copolymers which have been prepared using no monomers containing atleast 2 polymerizable double bonds are of course also suitable for thecoating agents according to the invention.

Compounds which can advantageously be used as component 1₂ are those ofthe general formula ##STR1## in which: R denotes H or CH₃, X denotes O,NR' or S, where R' denotes H, alkyl or aryl, and n denotes 2 to 8.

Examples of such compounds are hexanediol diacrylate, hexanedioldimethacrylate, ethylene glycol diacrylate, ethylene glycoldimethacrylate, butanediol diacrylate, butanediol dimethacrylate,hexamethylenebismethacrylamide, trimethylolpropane triacrylate,trimethylolpropane trimethacrylate and similar compounds.

Combinations of the polyunsaturated monomers can of course also beemployed.

Other possible components 1₂ are reaction products of a carboxylic acidcontaining a polymerizable olefinically unsaturated double bond andglycidyl acrylate and/or glycidyl methacrylate. It is also possible toemploy a polycarboxylic acid or unsaturated monocarboxylic acidesterified with an unsaturated alcohol containing a polymerizable doublebond as component 1₂. Diolefins, such as divinylbenzene, can furthermorealso be employed. Reaction products of a polyisocyanate with alcohols oramines containing unsaturated polymerizable double bonds are alsoemployed as unsaturated monomers containing at least two polymerizableolefinic double bonds. The reaction product of one mole of hexamethylenediisocyanate and 2 moles of allyl alcohol may be mentioned as an exampleof these. The ethylenically polyunsaturated monomers can advantageouslybe diesters of polyethylene glycol and/or polypropylene glycol having anaverage molecular weight of less than 1,500, preferably less than 1,000,and acrylic acid and/or methacrylic acid.

Examples of suitable monomers containing carboxyl groups (component 1₁)are the compounds in the description of the copolymers which containcarboxyl groups and are prepared by means of bulk polymerization.

The choice of component 1₃ largely depends on the desired properties ofthe coating agents in respect of elasticity, hardness, compatibility andpolarity. Vinyl-aromatic compounds, hydroxyalkyl esters ofα,β-unsaturated carboxylic acids, alkyl esters of α, β-unsaturatedcompounds, monomers containing tertiary amino groups and otherethylenically unsaturated monomers as well as combinations of thesemonomers are suitable. Examples of suitable compounds are the compoundsin the descriptions of the bulk polymers containing carboxyl groups. Inrespect of further detail on the copolymers containing carboxyl groups,reference is furthermore made to the PCT application with theinternational publication number WO 87/02041, in which these copolymersare described in detail.

Analogously to the copolymers prepared by means of bulk polymerization,in the case of the copolymers prepared by means of solutionpolymerization the carboxyl groups can also be introduced by usingmonomers containing carboxyl groups and/or addition of carboxylic acidanhydrides onto copolymers containing hydroxyl groups. The tertiaryamino groups present if appropriate can also be introduced into thecopolymer in the most diverse ways. The copolymers which containcarboxyl groups and are prepared by means of solution polymerizationusually have number-average molecular weights of 1,500 to 6,000, acidnumbers of 15 to 200 mg of KOH/g, preferably 30 to 120 mg of KOH/g, andamine numbers of 0 to 50 mg of KOH/g, preferably 10 to 40 mg of KOH/g.

Finally, the copolymers which contain carboxyl groups and are describedin the as yet unpublished patent application DE 3918669 are alsosuitable as the essential binder component A.

These copolymers containing carboxyl groups have a number-averagemolecular weight of 2,000 to 8,000, an acid number of 15 to 200 mg ofKOH/g, preferably 30 to 120 mg of KOH/g, and an amine number of 0 to 50mg of KOH/g, preferably 10 to 40 mg of KOH/g. They can be prepared by aprocedure in which

I) a copolymer containing hydroxyl groups and if appropriate carboxylgroups has been prepared by means of free radical solutionpolymerization at temperatures of 130° to 200° C., preferably 150° to180° C., from

r₁) 5 to 25% by weight, preferably 10 to 19% by weight, of one or morevinyl esters of aliphatic monocarboxylic acids which contain 5 to 15 Catoms per molecule and are branched in the α-position,

r₂) 10 to 50% by weight, preferably 20 to 45% by weight, of one or morevinylaromatic hydrocarbons,

r₃) 5 to 40% by weight, preferably 15 to 35% by weight, of one or morehydroxyalkyl esters of α,β-unsaturated carboxylic acids and

r₄) 0 to 40% by weight of ethylenically unsaturated monomers containingcarboxyl groups and/or other ethylenically unsaturated copolymerizablemonomers,

the sum of the parts by weight of components r₁ to r₄ in each case being100% by weight, and

II. if appropriate the copolymer obtained in stage I has been reactedwith carboxylic acid anhydrides, the amount of carboxylic acidanhydrides employed being chosen so that the copolymer formed has a acidnumber of 15 to 200 mg of KOH/g, preferably 30 to 120 mg of KOH/g.

The solution polymerization of components r₁ to r₄ is carried out herein the presence of as a rule 0.1 to 5.0% by weight, based on the amountof monomer to be processed, of free radical initiator and preferably inthe presence of up to 2% by weight of regulator, based on the amount ofmonomer to be processed. The addition of the regulators and initiatorsand examples of suitable regulators and initiators have already beenmentioned in the description of the solution polymerization. Suitablesolvents are listed previously in this description.

Because of the different reactivity of the monomers employed, it isdecisive for the properties of the resulting copolymers for thepolymerization to be carried out as follows:

At least 60% by weight, preferably 100% by weight, of the total amountof component r₁ to be employed is first initially introduced into thereactor together with some of the total amount of solvent to be employedand the mixture is heated up to the particular reaction temperature. Theremainder of the solvent--as already described--is preferably addedgradually together with the catalyst. Any remainder of component r₁which still exists and the other monomers (components r₂, r₃ and r₄) aremetered into the initially introduced component r₁ within a monomeraddition time which is the same for all components (and is in general2-10 hours, as is usual for acrylate copolymerizations) as follows:

i) The amount added per unit time of component r₁ which may still exist(that is to say the remainder of component r₁ which has not beeninitially introduced) remains constant or decreases within the monomeraddition time, the latter process variant being preferred. In the casewhere a constant amount is added, component r₁ is preferably metered intogether with components r₃ and r₄.

ii) The amount added per unit time of components r₃ and r₄ remainsconstant within the monomer addition period.

iii) The amount added per unit time of component r₂ is varied within themonomer addition time such that the total amount of component r₂ addedwithin the first third of the monomer addition time is 15 to 30% byweight, preferably 18 to 26% by weight, of the total amount of componentr₂. Within the second third of the monomer addition time, a total of 25to 40% by weight, preferably 30 to 38% by weight, is metered in, andwithin the last third of the monomer addition time 35 to 60% by weight,preferably 40 to 50% by weight, of the total amount of component r₂ ismetered in, the sum of the amounts added in the 1st 2nd and 3rd third ofcourse being 100% by weight.

There are various possibilities for varying the amount added per unittime of component r₂, it merely being decisive that the abovementionedtotal amounts added in the particular third being observed. Thus, forexample, there is the possibility of a stepwise change in the amountadded per unit time of component r₂. The number of steps in which theparticular amount added is changed can be chosen as desired. Thus, forexample, the amount added per unit time of component r₂ can be increasedonly at the start of the second and/or at the start of the third third.The amount added per unit time then in each case remains constant withinthe third. However, it is also possible for the amount added per unittime of component r₂ to be changed continuously, corresponding to thelimiting case of an infinite number of steps.

It is assumed that the addition of the components in the mannermentioned promotes the copolymerization and reduces homopolymerizationof the individual components. In addition, copolymers having a very lowresidual monomer content are obtained, resulting in clear solutionshaving a high solids content.

The resulting copolymers, containing carboxyl groups if appropriate,preferably have an average molecular weight of 1,500 to 8,000(number-average), and an OH number of 30 to 200 mg of KOH/g, preferably70 to 150 mg of KOH/g. The resulting copolymers containing hydroxylgroups and if appropriate containing carboxyl groups are then reactedwith carboxylic acid anhydrides in a second step to give thecorresponding copolymers containing carboxyl groups. The amount ofcarboxylic acid anhydride employed here is chosen so that the resultingcopolymer has an acid number of 15 to 200 mg of KOH/g, preferably 30 to120 mg of KOH/g, and an OH number of 0 to 60 mg of KOH/g. Thenumber-average molecular weight of the copolymer containing carboxylgroups is 2,000 to 8,000.

In addition to this preferred variant of introducing at least some ofthe carboxyl groups of the copolymer by addition of carboxylic acidanhydrides onto copolymers containing hydroxyl groups (obtained in stageI), there is of course also the possibility of incorporating thecarboxyl groups into the copolymer by using corresponding amounts ofmonomers containing carboxyl groups as component r₄ directly in thepolymerization.

Tertiary amino groups which are present if appropriate can be introducedinto the copolymer in the most diverse ways.

The following statements may be made on the components r₁ to r₄ employedin this solution polymerization process:

Vinyl esters of monocarboxylic acids, preferably vinyl esters ofmonocarboxylic acids which contain 5 to 15 C atoms per molecule and arebranched in the α-position, are employed as component r₁. The branchedmonocarboxylic acids can be obtained by reaction of formic acids orcarbon monoxide and water with olefins in the presence of a liquid,strongly acid catalyst; the olefins can be products obtained by crackingparaffinic hydrocarbons, such as mineral oil fractions, and can containboth branched and straight-chain acyclic and/or cycloaliphatic olefins.When such olefins are reacted with formic acid or with carbon monoxideand water, a mixture of carboxylic acids in which the carboxyl grouppredominantly sits on a quaternary carbon atom is formed. Other olefinicstarting substances are, for example, propylene trimer, propylenetetramer and diisobutylene The vinyl esters can also be prepared in amanner which is known per se from the acids, for example by reacting theacids with acetylene.

Vinyl esters of saturated aliphatic monocarboxylic acids which have 9-11C atoms and are branched on the α-C atom are particularlypreferred--because of their good availability. The vinyl ester ofp-tert.-butyl-benzoic acid is also particularly preferred. Examples ofother suitable vinyl esters are vinyl acetate and vinyl propionate.

Examples of the compounds suitable as components r₂ to r₄ are thecompounds already listed in the description of the solution polymerscontaining carboxyl groups, although no monomers containing at least twopolymerizable double bonds can be employed as component r₄.

In addition to these polyesters and/or copolymers containing carboxylgroups which have been described, other polymers which contain carboxylgroups and have a number-average molecular weight of 500 to 8,000 and anacid number of 15 to 200 mg of KOH/g can of course also be employed aslong as they lead to the desired properties of the coating agents. Thecoating agents contain the copolymer containing carboxyl groups(component A) in an amount of 10-70% by weight, based on the totalweight of the coating agents. The copolymers containing epoxide groups(component B) are usually employed in an amount of 10 to 50% by weight,based on the total weight of the coating agents. The contents of organicsolvents is 20 to 50% by weight, based on the total weight of thecoating agents.

If appropriate, the coating agents can also contain a crosslinkingcatalyst. Tertiary amines, quaternary ammonium compounds, such as, forexample, benzyltrimethylammonium hydroxide and benzyltrimethylammoniumchloride, and specific chromium compounds as well as tin compounds areparticularly suitable for this. The use of a crosslinking catalyst is ofcourse superfluous in most cases in which tertiary amino groups arealready incorporated in the acrylate copolymer. Lower stovingtemperatures and shorter stoving times are achieved by using an internalor external crosslinking catalyst. The cross linking catalyst ispreferably used in an amount of 0.5 to 10% by weight, based on the totalweight of the di- or polyepoxide component and the binder component.

The coating agents according to the invention can furthermore alsocontain the customary pigments and fillers in the customary amounts,preferably 0 to 60% by weight, based on the total composition, and othercustomary auxiliaries and additives, such as, for example, flow controlagents, silicone oils, plasticizers, such as phosphoric acid esters andphthalic acid esters, viscosity-regulating additives, delusteringagents, UV absorbers and light stabilizers, in the customary amounts,preferably 0 to 10% by weight, based on the total composition.

These coating agents can be applied in the form of a film to a substrateby spraying, flooding, dipping, rolling, knife-coating or brushing, thefilm subsequently being hardened to a firmly adhering coating.

The coating agents according to the invention are suitable forautomobile series painting and--if low hardening temperatures of between20° and 80° C. can be used by appropriate choice of the hardenercomponent (see above)--are also particularly suitable for refinishing ofmotor vehicles. They are employed in this context as a primer and a topor clear coat. The coating agents according to the invention areprepared by mixing the binders and crosslinking agents, if appropriatewith addition of solvent. Pigments and/or fillers can be added, ifappropriate, to the binder or the crosslinking agent by customaryprocesses (dispersing, dissolvers and the like). Other additivesemployed if appropriate can be added both to the binder or to thecrosslinking agent as well as to the finished coating agent.

The present invention thus also relates to a process for the preparationof coating agents containing

A) one or more polymers which contain carboxyl groups and have anumber-average molecular weight M_(n) of 500 to 8,000 and an acid numberof 15 to 200 mg of KOH/g as the essential binder component and

B) one or more compounds containing epoxide groups as the crosslinkingagent,

in which the binder component A and the crosslinking agent B are mixedonly shortly before application of the coating agents, wherein thecompound B containing epoxide groups is a copolymer which containsepoxide groups, has a number-average molecular weight M_(n) of 300 to5,000, preferably 500 to 3,500, and a heterogeneity (M_(w) /M_(n)),measured by gel permeation chromatography, of ≦3, preferably ≦2, and hasbeen prepared by continuous bulk polymerization at temperatures between130° and 350° C. and pressures above 1 bar.

The invention is illustrated in more detail in the following examplesAll the parts and percentage data are weight data, unless expresslystated otherwise.

I.1. Preparation of the Epoxy Crosslinking Agent

A mixture of 15 parts of styrene, 40 parts of glycidyl methacrylate and45 parts of n-butyl acrylate is heated at 230° C. in a continuouslyoperating pressure autoclave. The residence time of the reaction mixtureis 10 minutes. The pressure in the polymerization apparatus is kept inthe range between 15 and 32 bar with the aid of a periodicallyoscillating pressure regulation. The reaction mixture is then forcedthrough a static mixer for after-polymerization at 200° C. over aresidence time of 15 minutes. Unreacted monomers are then distilled offin vacuo.

The epoxy resin is then dissolved in butyl acetate to give an 80%solution. The resulting resin solution has a viscosity of 25 s, measuredin a DIN 4 flow cup at 23° C. The resulting epoxy resin has an epoxideequivalent weight of 316, based on the solid resin, a number-averagemolecular weight of 1,200 and a heterogeneity M_(w) /M_(n) of 1.9,determined against a polystyrene standard by the method described in B.Vollmert, Grundriβ der makromolekularen Chemie (Principles ofmacromolecular chemistry), E. Vollmert Verlag, Karlsruhe 1982, VolumeIII, page 72 et seq.

II.1. Preparation of the Binder Component A Containing Carboxyl Groups

482.2 parts of hexahydrophthalic anhydride, 585.3 parts of1,4-cyclohexanedicarboxylic acid, 611.8 parts of trimethylolpropane,123.1 parts of hexane-1,6-diol, 155.2 parts of methyldiethanolamine,79.6 parts of benzoic acid, 206.1 parts of isononanoic acid, 87.8 partsof xylene and 2.196 parts of triisodecyl phosphite are introduced into a4 liter polycondensation kettle with a stirrer, steam-heated column andwater separator and are slowly heated up. The condensation is carriedout at a temperature of not more than 190° C. to an acid number of 9.1mg of KOH/g and a viscosity of 4.2 dPas (50% in butylglycol), and theproduct is then cooled and partly dissolved with 387.4 parts of xyleneat 130° C. 367.0 parts of hexahydrophthalic anhydride, 80.9 parts ofxylene and 0.742 part of triisodecyl phosphite are now added to thissolution. The anhydride is added at 80° C., until an acid number of 69.4mg of KOH/g and a viscosity of 8 dPas (50% in butylglycol) is reached.The product is then partly dissolved with 718.6 parts of xylene and182.1 parts of sec.-butanol. The polyester thus obtained has a solidscontent of 59.7%, an acid number of 67 mg of KOH/g (solid), an aminenumber of 31 mg of KOH/g, a viscosity (original) of 27.5 dPas and acolor number of 1-2 (Gardner-Holdt).

II.2. Preparation of the Binder Component B Containing Carboxyl Groups

The following components are weighed into a 4 liter stainless steelpolymerization kettle with a stirrer, reflux condenser, two monomerfeeds and an initiator feed and heated up to 100° C. 484.0 parts ofxylene and 161.0 parts of 1-methoxypropyl 2-acetate. The following areweighed into monomer feed A: 80.0 parts of dimethylaminoethylmethacrylate, 90.0 parts of xylene and 30 0 parts of 1-methoxypropyl2-acetate.

The following are weighed into monomer feed B: 143.0 parts of methylmethacrylate, 120.0 parts of n-butyl acrylate, 120.0 parts of cyclohexylmethacrylate, 120.0 parts of 4-hydroxybutyl acrylate, 120.0 parts ofhydroxyethyl methacrylate, 97.0 parts of divinylbenzene (62% strength inethylstyrene), 22.4 parts of mercaptoethanol and 0.24 part oftriisodecyl phosphite.

The following are weighed into the initiator feed: 19.2 parts of2,2'-azobis(2-methylbutane-nitrile), 58.0 parts of xylene and 19.2 partsof 1-methoxypropyl 2-acetate.

All the feeds are started at the same time and the two monomer feeds aremetered in uniformly in the course of 3 hours and the initiator feed ismetered in over a period of 3.75 hours. The temperature in the kettle iskept at 108° to 100° C. during the polymerization. After-polymerizationis then carried out for a further 2 hours. The resulting acrylate resinsolution has a solids content of 51% and a viscosity of 24 dPas. 169.0parts of hexahydrophthalic anhydride are now introduced and added ontothe acrylate resin at 100° C. When the acid number determination resultsin the same values in aqueous and alcoholic KOH, the mixture isconcentrated to a solids content of 55-56% by distilling off solventsand is then diluted to a solids content of 51% with sec.-butanol. Theacrylate resin solution thus obtained has an acid number of 72 mg ofKOH/g and a viscosity of 27 dPas, as well as an amine number of 28.6 mgof KOH/g.

II.3. Preparation of the Binder Component C Containing Carboxyl Groups

The following components are weighed into a 4 liter stainless steelpolymerization kettle with a stirrer, reflux condenser, two monomerfeeds and an initiator feed and are heated up to 100° C.: 382.0 parts ofxylene and 382.0 parts of 1-methoxypropyl 2-acetate.

The following are weighed into the monomer feed A: 82.0 parts ofdimethylaminoethyl methacrylate, 350.0 parts ofmono-2-methacryloyloxyethyl hexahydrophthalate, 100.0 parts of xyleneand 100.0 parts of 1-methoxypropyl 2-acetate.

The following are weighed into monomer feed B: 148.0 parts of butylmethacrylate, 124.0 parts of n-butyl acrylate, 124.0 parts of cyclohexylmethacrylate, 72.0 parts of hydroxypropyl methacrylate, 100.0 parts ofdivinylbenzene (62% in ethylstyrene), 24.0 parts of mercaptoethanol and0.53 part of triisodecyl phosphite.

The following are weighed into the initiator feed: 20.0 parts of2,2'-azobis(2-methylbutane-nitrile), 40.0 parts of xylene and 40.2 partsof 1-methoxypropyl 2-acetate.

The monomer feeds are started at the same time, and the initiator feedis started 10 minutes later. The two monomer feeds are metered inuniformly in the course of 3 hours, and the initiator feed is metered inover a period of 3.75 hours. The temperature in the kettle is kept at108°-110° C. during the polymerization. After-polymerization is thencarried out for a further 2 hours. The mixture is concentrated to asolids content of about 60% by distilling off the solvent, and is thendiluted with sec.-butanol. The acrylate resin solution thus obtained hasa solids content of 51% and an acid number of 67 mg of KOH/g, as well asan amine number of 34 mg of KOH/g.

II.4. Preparation of the Binder Component D Containing Carboxyl Groups

425.75 parts of Shellsol A® (mixture of C3-C4-alkyl-substitutedaromatics) and 400 parts of a commercially available mixture of vinylesters of saturated aliphatic monocarboxylic acids which predominantlyhave 10 C atoms and are branched on the α-C atom are initiallyintroduced into a 4 liter stainless steel kettle with a stirrer, refluxcondenser and feed devices, and are heated up to 170° C.

The following are weighed into monomer tank I and mixed: 600.0 parts ofhydroxyethyl methacrylate, 250.0 parts of n-butyl acrylate, 150.0 partsof N,N'-dimethylaminoethyl methacrylate, 200.0 parts of butylmethacrylate and 4.1 parts of triisodecyl phosphite.

The following are weighed into monomer tank II and mixed: 400 parts ofstyrene.

The following are weighed into the initiator tank and mixed: 22.0 partsof dicumyl peroxide and 66.0 parts of Shellsol A®.

The contents of monomer tank I and the initiator tank are metered inuniformly in the course of 4.5 hours. The contents of monomer tank IIare metered in over a period of 4.5 hours such that 100 parts aremetered during the first 90 minutes, 140 parts are metered from the 91stto the 180th minute of the total running time and 160 parts of styreneare metered during the remaining feed time. During the feed, thetemperature in the kettle is kept at 165°-170° C. When the feeds haveended, a further 5.0 parts of dicumyl peroxide and 15.0 parts ofShellsol A®are metered in from the initiator tank in the course of 1hour. After-polymerization is then carried out at this temperature for afurther 2 hours. The product is then partly dissolved with 361 parts ofxylene. The non-volatile content (1 hour, 130° C.) of this copolymersolution is 70% and the viscosity of the solution (50% in butyl acetate)is 3.25 dPas at 23° C.

1325.0 parts of this acrylate resin solution are weighed into a 4 literstainless steel kettle with a stirrer and reflux condenser. Afteraddition of 221.4 parts of hexahydrophthalic anhydride, the mixture isheated up to 130° C. and kept at this temperature until the acid numbersin an alcoholic and in an aqueous medium are the same and are 70-72 mgof KOH/g. The copolymer solution is partly dissolved to a solids contentof 65% with 221.25 parts of xylene and further diluted with 321.5 partsof sec.-butanol.

The non-volatile content (1 hour, 130° C.) of this copolymer solution is55% and the viscosity of the solution (50% in butyl acetate) is 24.5dPas at 23° C. (ICI plate/cone viscosity). The copolymer has an acidnumber of 70 mg of KOH/g and an amine number of 24 mg of KOH/g.

II.5. Preparation of Binder Component E Containing Carboxyl Groups

419.75 parts of Shellsol A® (mixture of C3-C4alkyl-substitutedaromatics) and 300 parts of a commercially available mixture of vinylesters of saturated aliphatic monocarboxylic acids which predominantlyhave 10 C atoms and are branched at the α-C atom are initiallyintroduced into a 4 liter stainless steel kettle with a stirrer, refluxcondenser and feed devices and are heated up to 170° C.

The following are weighed into monomer tank I and mixed: 700.0 parts ofhydroxyethyl methacrylate, 200.0 parts of n-butyl acrylate, 200.0 partsof methyl methacrylate and 20.0 parts of mercaptoethanol.

The following are weighed into monomer tank II and mixed: 600.0 parts ofstyrene.

The following are weighed into the initiator tank and mixed: 26.0 partsof dicumyl peroxide and 78.0 parts of Shellsol A®.

The contents of monomer tank I and of the initiator tank are metered inuniformly in the course of 4.5 hours. The contents of monomer tank IIare metered in over a period of 4.5 hours such that 100 parts aremetered in the first 90 minutes, 140 parts are metered from the 91st tothe 180th minute of the total running time and 160 parts of styrene aremetered in the remaining feed time. During the feed, the temperature inthe kettle is kept at 165 to 170° C. When the feeds have ended, afurther 5.0 parts of dicumyl peroxide and 15.0 parts of Shellsol A® aremetered in from the initiator tank in the course of 1 hour.After-polymerization is then carried out at this temperature for afurther 2 hours. The product is subsequently partly dissolved with 427.3parts of xylene and 427.3 parts of 1-methoxypropyl 2-acetate. Thenon-volatile content (1 hour, 130° C.) of this copolymer solution is 60%and the viscosity of the solution (50% in butyl acetate) is 10.80 dPasat 23° C. (ICI plate/cone viscosity).

1560.0 parts of this acrylate resin solution are weighed into a 4 literstainless steel kettle with a stirrer and reflux condenser. Afteraddition of 222.7 parts of hexahydrophthalic anhydride, the mixture isheated up to 130° C. and kept at this temperature until the acid numbersin an alcoholic and in an aqueous medium are the same and are 70-72 mgof KOH/g.

The mixture is then cooled to 60° C., and 296.6 parts of a 1:1 adduct ofN,N'-dimethylethanolamine and isophorone diisocyanate and 12.9 parts ofdibutyltin dilaurate are added. The temperature is kept at 60° C. untilfree isocyanate can no longer be detected. The copolymer solution isdiluted to a solids content of 50% with 462.3 parts of sec.-butanol. Thecopolymer solution thus obtained has an acid number of 63 mg of KOH/g, aviscosity of 8.5 dPas at 23° C. and an amine number of 24 mg of KOH/g.

EXAMPLES 1-4

Coating agents 1 to 4 are prepared by mixing the epoxide crosslinkingagent with the binder components containing carboxyl groups in theamounts stated in Table 1. These coating agents are adjusted to a flowviscosity of 25 s, measured in a DIN 4 cup at 23° C., with butylacetate. The coating agents are applied to glass plates in a wet filmthickness of 100 μm, dried under various conditions and then evaluated.Drying is carried out by

a) storage at room temperature for 2 days or

b) 30 minutes at 60° C. and subsequent storage at room temperature for 1hour or

c) 30 minutes at 100° C. and subsequent storage at room temperature for1 hour.

On drying at room temperature (drying a), the resulting coatings alreadyshowed an absence of dust and tackiness after less than 2 hours. Thecoatings moreover showed in each case good resistance to petrol, a highgloss and a good hardness coupled with good flexibility with all thedrying methods a, b or c.

                  TABLE 1                                                         ______________________________________                                        Compositions of coating agents 1 to 4 in parts by weight                                 Coating                                                                              Coating  Coating  Coating                                              agent 1                                                                              agent 2  agent 3  agent 4                                   ______________________________________                                        Crosslinking agent                                                                         50       25.3     10     25.3                                    Binder component A                                                                         55       --       --     --                                      Binder component B                                                                         129      --       --     --                                      Binder component C                                                                         --       42.6     --     --                                      Binder component D                                                                         --       --       28.5   --                                      Binder component E                                                                         --       --       --     44.45                                   ______________________________________                                    

We claim:
 1. A coating agent comprising:A) a polymer selected from thegroup consisting of a copolymer containing carboxyl groups, a polyestercontaining carboxyl groups and mixtures thereof, said polymer having anumber-average molecular weight M_(n) of 500 to 8,000 and an acid numberof 15 to 200 mg of KOH/g as the essential binder component; and B) atleast one compound containing epoxide groups as crosslinking agents;wherein the compound B containing epoxide groups is a copolymercontaining epoxide groups, has a number-average molecular weight M_(n)of 300 to 5,000 and a heterogeneity (M_(w) /M_(n)), measured by gelpermeation chromatography, of ≦3 and has been prepared by continuousbulk polymerization at temperatures between 130° and 350° C. andpressures above 1 bar ofa) 10 to 60% by weight of at least onevinylaromatic hydrocarbon; b) 10 to 50% by weight of at least oneethylenically unsaturated monomer containing at least one epoxide groupper molecule; and c) 5 to 80% by weight of other ethylenicallyunsaturated copolymerizable monomers; the sum of the weight contents ofcomponents (a) to (c) in each case being 100% by weight.
 2. A processfor the preparation of a coating agent comprising:A) a polymer selectedfrom the group consisting of a copolymer containing carboxyl groups, apolyester containing carboxyl groups and mixtures thereof, said polymerhaving a number-average molecular weight M_(n) of 500 to 8,000 and anacid number of 15 to 200 mg of KOH/g as the essential binder componentand B) one or more compounds containing epoxide groups as thecrosslinking agent, which comprises:mixing the binder component A andthe crosslinking agent B only shortly before application of the coatingagent, wherein the compound B containing epoxide groups is a copolymerwhich contains epoxide groups, has a number-average molecular weightM_(n) of 300 to 5,000, and a heterogeneity (M_(w) /M_(n)), measured bygel permeation chromatography, of ≦3, and has been prepared bycontinuous bulk polymerization at temperatures between 130° and 350° C.and pressures above 1 bar ofa) 10 to 60% by weight of one or morevinylaromatic hydrocarbons, b) 10 to 50% by weight of one or moreethylenically unsaturated monomers containing at least one epoxide groupper molecule and c) 5 to 80% by weight of other ethylenicallyunsaturaged copolymerizable monomers, the sum of the weight contents ofcomponents (a) to (c) in each case being 100% by weight.
 3. A coatingagent as claimed in claim 1, wherein the compound B has a number-averagemolecular weight M_(n) of 500 to 3,500.
 4. A coating agent as claimed inclaim 1, wherein the compound B has a heterogeneity (M_(w) /M_(n)),measured by gel permeation chromatographly, of ≦2.
 5. A coating agent asclaimed in claim 1, wherein the copolymer B containing epoxide groupshas been prepared by bulk polymerization ofa) 15 to 50% by weight, ofone or more vinylaromatic hydrocarbons, b) 15 to 50% by weight of one ormore ethylenically unsaturated monomers containing at least one epoxidegroup per molecule and c) 20 to 50% by weight, of other ethylenicallyunsaturated copolymerizable monomers,the sum of the weight contents ofcomponents (a) to (c) in each case being 100% by weight.
 6. A coatingagent as claimed in claim 1, wherein the copolymer B containing epoxidegroups has been prepared using glycidyl methacrylate as one of theethylenically unsaturated monomers.
 7. A coating agent as claimed inclaim 1, wherein the copolymer B containing epoxide groups has beenprepared using alkyl esters selected from the group consisting ofacrylic acid, methacrylic acid or mixtures thereof as one of theethylenically unsaturated monomers.
 8. A coating agent as claimed inclaim 1, wherein the copolymer B containing epoxide groups has anepoxide equivalent weight of 150 to 2,000.
 9. A coating agent as claimedin claim 8, wherein the copolymer B containing epoxide groups has anepoxide equivalent weight of 500 to 1,000.
 10. A coating agent asclaimed in claim 1, wherein the polymers which contain carboxyl groupsand are employed as the binders A have an acid number of 30 to 120 mg ofKOH/g.
 11. A coating agent as claimed in claim 1, wherein the polymerswhich contain carboxyl groups and are employed as the binders A have anamine number of 0 to 50 mg of KOH/g.
 12. A coating agent as claimed inclaim 1, wherein the polymers which contain carboxyl groups and areemployed as the binders A have an amine number of 10 to 40 mg of KOH/g.13. A coating agent as claimed in claim 1, wherein the polymers whichcontain carboxyl groups and are employed as the binders A have beenprepared by a procedure in which a polymer containing hydroxyl groupsand having an OH number of 30 to 200 mg of KOH/g has first been preparedand has then been reacted with carboxylic acid anhydrides to give thecorresponding polymers containing carboxyl groups.
 14. A coating agentas claimed in claim 1, wherein the polymers which contain carboxylgroups and are employed as the binders A have likewise been prepared bycontinuous bulk polymerization at temperatures between 130° and 350° C.and pressures above 1 bar.
 15. A coating agent as claimed in claim 1,wherein the polymers which contain carboxyl groups and are employed asthe binders A are copolymers prepared by free radical solutionpolymerization.
 16. A coating agent as claimed in claim 1, wherein thecoating agent contains:A) 10 to 70% by weight, based on the total weightof the coating agent, of binder A containing carboxyl groups; B) 10 to50% by weight, based on the total weight of the coating agent, ofcrosslinking agent B containing epoxide groups; C) 20 to 50% by weight,based on the total weight of the coating agent, of one or more organicsolvents; and D) 0 to 60% by weight, based on the total weight of thecoating agent, of pigments and fillers; and E) 0 to 10% by weight, basedon the total weight of the coating agent, of customary auxiliaries andadditives.
 17. A process for automobile repair refinishing, wherein acoating agent as claimed in claim 1 is applied.
 18. A process forautomobile series painting, where a coating agent as claimed in claim 17is applied.